How is the rate law for for A+B = X -> C written?

Considering the following reaction:

A + B k^*

k^-* X k^**

C

Do I have to describe the consumption speed of X by:

d(X)/dT= k^*(A)(B) - k^-*(X) - k^**(C)
d(X)/dT= k^*(A)(B) - k^-*(X)
or are both correct?
Serge Gomes (100572.3605@compuserve.com)

X is produced by the process you've labelled with '*' and destroyed by the processes labelled '-*' and '**'. If these are one-step processes, the net rate of change for X should be

d(X)
dt = k^*(A)(B) - k^-*(X) - k^**(X)

so unless k^** is very small, the answer is 'none of the above'.

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How is the rate law for for A+B = X -> C written?